Methane, a potent greenhouse gas, is converted to CO2 by microbes in tree bark, meaning trees are even better for the climate than we thought
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| Manu National Park in Peru, where some measurements were taken for the study (Credit: Vincent Gauci) |
Microbes living in the bark of trees are absorbing methane from the air, making trees about 10 per cent better for the climate than previously thought.
Methane is a greenhouse gas that is responsible for about a quarter of human-caused global warming.
Scientists have already shown that some trees growing in water-logged soils can emit methane that was generated underground. But the presence of methane-eating microbes known as methanotrophs in tree bark suggests trees could also be a net sink for atmospheric methane.
Methanotrophs consume methane as their source of carbon and chemical energy, producing carbon dioxide and organic compounds.
Vincent Gauci at the University of Birmingham, UK, and his colleagues took measurements from trees growing in well-drained soils around the world, measuring the methane exchange between the atmosphere and the tree bark at multiple heights.
They found that, while at soil level most trees emit small amounts of methane, further up the trunk the exchange flips and trees start absorbing atmospheric methane.
The methanotrophs produce carbon dioxide from the process, but this is a much less potent greenhouse gas than methane, says Gauci. “There’s tremendous benefit in that conversion to CO2,” he says.
The findings demonstrate, for the first time, that methanotrophs are removing methane from the atmosphere at a large scale, across temperate, boreal and tropical environments.
Trees growing in tropical locations are about 12 per cent better for the climate, once this methane-absorbing effect is factored in, while trees in temperate locations are about 7 per cent better. In total, trees could be absorbing between 24 million and 50 million tonnes of methane from the atmosphere each year, similar to the volume absorbed by the world’s soils.
“Existing forests are that much more important than we thought, and we should preserve them,” concludes Gauci. He is now working to understand whether trees can be bio-hacked to support the activities of methanotrophs, to boost their methane-absorbing abilities.
Luke Jeffrey at Southern Cross University, Australia, says the findings suggest trees act as a “substantial natural sink for atmospheric methane”. “Future work will help to determine the magnitude of methane uptake by tree woody surfaces, which may bolster the ecological values of trees and increase their importance as natural climate solutions,” he says.
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